1. Field of the Invention
The present invention relates to a photomask used in manufacturing high density integrated circuits and the like, including LST and VLSI, and to a blank for a photomask for manufacturing the photomask, and particularly relates to a halftone phase shift photomask in which a projected picture in minute dimensions can be obtained and a blank for a halftone phase shift photomask to facilitate the manufacture of the phase shift photomask.
2. Description of the Related Art
Semiconductor integrated circuits such as IC, LSI and VLSI are manufactured by repeating a lithography process using a photomask. Particularly, the use of a phase shift photomask as shown in, for example, EP 0 090 924A2 (JP-A-58-173744, JP-B-62-59296) has been considered in order to form a circuit with minute dimensions.
Various kinds constructions have been proposed as the phase shift photomask. Particularly, in view of the possibility of practical use in early stage, halftone phase shift photomasks such as shown in, for example, JP-A-4-136854, U.S. Pat. No. 4,890,309 has been widely noticed.
Further, as disclosed in JP-A-5-2259, and JP-A-5-127361, some proposals have been made for construction and materials for increasing the yield and cost reductions may result by virtue of the reduced number of steps in the manufacturing processes.
As described below in detail, the halftone phase shift photomask comprises a transparent substrate, a halftone phase shift film, and optionally a light shading film.
In a halftone phase shift lithography, an area would be caused where the adjoining shots (transferring ranges by each exposure) on a wafer overlap each other when the xe2x80x9cstep-and-repeatxe2x80x9d exposure, using equipment such as a stepper or scanner, is performed. Since the remaining pattern parts, differing from a conventional chromium mask, are also semitransparent, the overlapped areas are exposed to light by repeating multiple exposures.
Further, in a halftone phase shift lithography, there was a problem such that a subpeak in light intensity might occur in the neighborhood of an exposure pattern to be transferred when a wafer was exposed, and thus the subpeak may deform the exposure pattern predefined.
This problem is remarkable especially in the neighborhood of a large come-off pattern. Consequently, in a large come-off pattern which can be sufficiently resolved without using a phase shift lithography technique, its transferring property is rather inferior to a conventional type of using chromium mask.
For solutions to these problems, a halftone phase shift lithography method is generally adopted in transferring to a wafer, in which a halftone phase shift mask is used where a halftone phase shift film and a light shading film (which involves films of giving substantially complete light shading and film by which high contrast can be obtained, hereafter also referred to as a xe2x80x9clight shading layerxe2x80x9d or a xe2x80x9csubstantial light shading filmxe2x80x9d), both of which being patterned with the predetermined pattern, are layered onto the substrate in this order.
A halftone phase shift mask having such a light shading film is manufactured by using a blank where a halftone phase shift film and a light shading film are layered in this order onto a transparent substrate, and patterning the light shading film, separately from the patterning of a halftone phase shift film.
In the following, the conventional and typical manufacturing method of a halftone phase shift mask having the light shading film will be briefly explained.
First, on a blank in which a halftone phase shift film and a light shading film has been layered in this order on a transparent substrate in advance, a desired first resist pattern is formed by using the conventional lithography technique. Then, by using the first resist pattern as an anti-etching mask, both of a halftone phase shift pattern and a light shading film pattern are etched in a first etching step where the light shading film and the halftone phase shift film are etched sequentially in this order.
After the first etching step, following the removal of the first resist pattern and the rinsing of the substrate, a second resist pattern is further formed by using the conventional lithography technique. Then, a second etching step is performed, wherein only the light shading film is etched and patterned by using the second resist pattern as another anti-etching mask in order to form the light shading film pattern.
In the first etching step, the whole pattern to be formed on the mask are formed, and in the second etching step, a pattern is formed so that a light shading film is removed only in an area where a halftone phase shift effect is required.
As materials for the halftone phase shift film, for the purpose of possessing good characteristics with respect to the film forming property, patterning property, chemical stability after patterning, and durability, various kinds of materials, for example, an oxide film or nitride film of tantalum as disclosed in JP-A-7-134396 and JP-A-7-281414, films of metal silicide based materials including tantalum silicide based materials as disclosed in JP-A-6-83027 and molybdenum silicide based materials as disclosed in JP-A-6-332152, U.S. Pat. No. 5,474,864 (JP-A-7-140635) and U.S. Pat. No. 5,482,799 (JP-A-7-168343), films of chromium based materials as disclosed in JP-A-7-5676, JP-A-6-308713, JP-A-7-28224 and JP-A-7-110572, have been proposed and already put into use commercially.
On the other hand, as material for the light shading films (films providing substantially complete light shielding or film of giving films providing high contrast), films of chromium based materials have been used in view of their film forming properties, processability, film stability and the like.
For shaping the halftone phase shift film, the dry etching technique may be generally used. The dry etching technique can be roughly divided into two types, i.e., chlorine types and fluorine types. In actual use, owing to the kind of materials used for the film, one type would be selected promptly and thus it is necessary to know how to use them properly.
When the halftone phase shift film is formed with a material of chromium based film, chlorine dry etching is used. Whereas, the fluorine dry etching is usually used when the halftone phase shift film is formed with one of metal silicide based materials including tantalum silicide and molybdenum silicide, or formed with tantalum based materials, although the chlorine dry etching may be used in some cases.
Next, chromium based materials which are used as the light shading films have to be dry etched by a chlorine based gas. Therefore, when using one etching chamber, the fluorine dry etching for a silicide used as the halftone phase shift film should be followed by a gas replacing operation in the course of the aforementioned first etching step, which can be observed in the conventional and typical manufacturing method of the halftone phase shift mask having the aforementioned light shading film, and which results in complexities of the process and the etching apparatus""s construction as well as troublesome operations.
By using two etching chambers, it would be possible to modify the first etching step so that the dry etching of the light shading film in an etching chamber is followed by the transfer of the treated substrate from the chamber to another chamber in order to dry-etch the silicide in the latter chamber. That is, it is possible to take such a way that the first etching step is discontinued in its course so as to transfer the substrate to the next chamber. However, the way also results in complexity of the etching apparatus""s construction, and an enhancement in cost.
As described above, with respect to a halftone phase shift mask, it has been desired that a light shading film (a film of giving substantially complete light shading or film by which high contrast is obtained) and a halftone phase shift film can be dry-etched with using a gas, or gases of the same type regardless of the material types of the halftone phase shift film.
Accordingly, the present invention is aimed at providing a new halftone phase shift photomask. Further, the present invention is aimed at a halftone phase shift photomask having a constitution such that a dry etching process can be carried out without using a complex process and complex constitution in an etching equipment. Further more, the present invention is aimed at providing a blank for a halftone phase shift photomask which will make such a processing possible.
A blank for a halftone phase shift photomask according to the present invention is a blank for forming a halftone phase shift photomask and which comprises a transparent substrate, a halftone phase shift layer and a substantial light shielding film, the halftone phase shift layer and the substantial light shielding film being layered on the transparent substrate, and the substantial light shielding film being a single layered or multiple layered film which has a layer containing tantalum as a main ingredient.
In an embodiment of the blank according to the present invention, the halftone phase shift layer is a single layered or multiple layered film which has a layer containing a metal silicide as a main component and further containing element(s) selected from the group consisting of oxygen, nitrogen and fluorine. In a preferred embodiment of the present invention, the metal silicide is tantalum silicide.
In another embodiment of the blank according to the present invention, the halftone phase shift layer is a single layered or multiple layered film which has a layer containing chromium as a main component and further containing element(s) selected from the group consisting of oxygen, nitrogen and fluorine.
In still other embodiment of the blank according to the present invention, the halftone phase shift layer is formed on the transparent substrate so as to have a phase difference xcfx86 within the range of nxcfx80xc2x1xcfx80/3 radian (n is an odd number), the phase difference xcfx86 being calculated from the following equation:       φ    =                            ∑                      k            =            1                                m            -            1                          ⁢                  xc3x97                      (                          k              ,                              k                +                1                                      )                              +                        ∑                      k            =            2                                m            -            1                          ⁢                  xe2x80x83                ⁢                  2          ⁢                      π            ⁡                          (                                                u                  ⁡                                      (                    k                    )                                                  -                1                            )                                ⁢                                    d              ⁡                              (                k                )                                      /            λ                                ⁢      xe2x80x83  
wherein xcfx86 is a phase change caused to light vertically transmitting through the photomask in which a halftone phase shift layer having (mxe2x88x922) layer(s) is disposed on the transparent substrate, xc3x97(k, k+1) is a phase change occurring in the interface between a kth layer and a (k+1)th layer, u(k) and d(k) are the refractive index and film thickness of a material forming the kth layer, respectively, and xcex is the wavelength of exposure light, providing that the layer of k=1 is the transparent substrate and the layer of k=m is air.
In another embodiment of the blank according to the present invention, the halftone phase shift layer is formed on the transparent substrate so as to have a film thickness with the transmittance of exposure light within the range of 1 to 50% when the transmittance of exposure light of the transparent substrate is defined as 100%.
The halftone phase shift photomask of the present invention is a halftone phase shift photomask which comprises a transparent substrate, a halftone phase shift layer and a substantial light shielding film, the halftone phase shift layer and the substantial light shielding film being layered on a transparent substrate, and the substantial light shielding film being a single layered or multiple layered film which has a layer containing tantalum as a main ingredient.
In an embodiment of the halftone phase shift photomask according to the present invention, the halftone phase shift layer is a single layered or multiple layered film which has a layer containing a metal silicide as a main component and further containing element(s) selected from the group consisting of oxygen, nitrogen and fluorine. In a preferred embodiment of the present invention, the metal silicide is tantalum silicide.
In another embodiment of halftone phase shift photomask according to the present invention, the halftone phase shift layer is a single layered or multiple layered film which has a layer containing chromium as a main component and further containing element(s) selected from the group consisting of oxygen, nitrogen and fluorine.
Instill other embodiment of halftone phase shift photomask according to the present invention, the halftone phase shift layer is formed on the transparent substrate so as to have a phase difference xcfx86 within the range of nxcfx80xc2x1xcfx80/3 radian (n is an odd number), the phase differences being calculated from the following equation:       φ    =                            ∑                      k            =            1                                m            -            1                          ⁢                  xc3x97                      (                          k              ,                              k                +                1                                      )                              +                        ∑                      k            =            2                                m            -            1                          ⁢                  xe2x80x83                ⁢                  2          ⁢                      π            ⁡                          (                                                u                  ⁡                                      (                    k                    )                                                  -                1                            )                                ⁢                                    d              ⁡                              (                k                )                                      /            λ                                ⁢      xe2x80x83  
wherein xcfx86 is a phase change caused to light vertically transmitting through the photomask in which a halftone phase shift layer having (mxe2x88x922) layer(s) is disposed on the transparent substrate, xc3x97(k, k+1) is a phase change occurring in the interface between a kth layer and a (k+1)th layer, u(k) and d(k) are the refractive index and film thickness of a material forming the kth layer, respectively, and xcex is the wavelength of exposure light, providing that the layer of k=1 is the transparent substrate and the layer of k=m is air.
In another embodiment of the halftone phase shift photomask according to the present invention, the halftone phase shift layer is formed on the transparent substrate so as to have a film thickness with the transmittance of exposure light within the range of 1 to 50% when the transmittance of exposure light of the transparent substrate is defined as 100%.
The blank for halftone phase shift photomask according to the present invention, because of having thus constitution, can provides the halftone phase shift photomask by using dry etching without complicating the etching process and the etching apparatus.
The halftone phase shift photomask according to the present invention, also can be manufactured by using dry etching without complicating the etching process and the etching apparatus.